Electromagnetic device



Aug. 10, 1937. H. A. BREDEHOFT 2,089,334

7 ELECTROMAGNETIC DEVICE Filed April 10, 1936 INVENTOR H. A. BRE DEHOF T A T TORNE V Patented Aug. 10, 1937 ELECTROMAGNETIC DEVICE Harold A. Bredehoft, Millington, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 10, 1936, Serial No. 73,671

. v 4 Claims.

.fI'his invention relates to electromagnetically operated devices and more particularly'to devices ofthis kindcommonly known as telephone ringers..--

'5 ---;.The object of this invention is to provide, in an I electromagnetically operated device, means for maintaining an armature in correct spaced relation relative to an attracting pole of an electromagnet. ,A; feature of this invention resides in spring means associatedwith the armature. In the drawing: ,Fig. 1 is a front elevational view of a polarized ringer of this invention showing the parts in norm si on;

Eig. Z is-a front elevational view of a portion of the polarized ringer shown in Fig. 1, a part being broken away to get a clearer view of the invention and-showing the armature in attracted e P s ti n; a d

,,Ilig. 3 is-a view in perspective of the spring. rlna telephonev ringer the armature is supported insome predetermined spaced relation to an attracting pole of an electromagnet, the correct ,spa cin'g,o f the armature from the attracting pole being important to obtain efiicient operation of the ringer, 1 ;After an armature has been attracted towarda pole of the electromagnet and the at- ,tractingforce is diminished or discontinued, it necessary that the armature be returned again .tonormal position. It is common practice in biased telephone ringer construction to attach .a spring to an armature and to a support, the springserving to withdraw the armature from the pole of .the electromagnet when the attractiveflforce of the electromagnet is diminished or discontinued. 7 It is also common practice in biased and unbiased telephone ringer constructions to provide a nonmagnetic element between an armature and theattracting pole of an electromagnet to prevent sticking of the armature to the pole of the" electroma gnet. -.Inf,unbiased telephone ringers now in use the return of the armature to normal position delpends largely on the quickness of decay of the attractive force in the pole of the electromagnet and the correct balancing of the armature in its supporting means. It sometimes happens in the operation of .unbiased telephone ringers that the ,;,50 pole of the electromagnet becomes so afiected by l the current supplied through the operating wind- ,ing that. it fails .to release the armature. This 'occursffor instanceQwhen a so-called comparativelylarge soak current is applied to the ringer. ;;55 Under such conditions the armature remains drawn toward the pole of the electromagnet even when a non-stick element is provided between the armature and the pole of the electromagnet. The ringer then fails to operate until the effect of the comparatively large soak current becomes 5 dissipated.

In this invention a spring of non-magnetic material is provided on the armature. The spring is located between the armature and the attracting pole of the electromagnet and serves as a 10 return spring and a non-stick element.

The invention is shown in the drawing as applied to a polarized ringer of the type disclosed in E. B. Craft Patent 1,096,287, May 12, 1914, and to which reference may be had for a detailed de- 15 scription of the construction of the ringer.

The ringer is provided with a permanent magnet I and an electromagnet 2 comprising the twospools 3 and 4 joined by a suitable yoke 30. The poles 5 and 6 project as indicated and are pro- 20 vided with annular grooves 1 and 8. The mounting for an armature 9 is supported on the projecting ends of the poles 5 and 6. This mounting comprises a forked or slotted brass plate Ill and a bridge member II, the free ends of the bridge 5 member ll engaging and resting upon the outer ends of the tangs of the brass plate In. The tangs of the brass plate It rest in the annular grooves I and 8 of the poles 5 and 6. A machine screw l2 extending through the bridge member H and threaded into a central aperture in the brass plate It] serves to hold the bridge member I I and the brass plate It) together. The bridge member H is provided with spaced ears, such as IS, in each of which is inserted a screw such as l8 and by means of which the armature 9 is pivotally supported at its center.

A substantially flat spring 3|, such as shown in Fig. 3 and of about the same length and Width as the armature 9, is attached at its central portion to the upper surface of the armature 9. The spring 31 is made of non-magnetic spring material and has flexible free end portions 32 and 33 offset from the plane of the central portion 34 and extending above the plane of the central portion 34 and parallel with the upper surface of the armature 9. Adjacent the points of offset 35 and 36 and in the free end portions 32 and 33 of the spring 3! are spaced projections 31. The projections 31 extend downward from the free end portions 32 and 33 of the spring 3| and into engagement with the upper surface of the armature 9 and serve as fulcrums for the free end portions 32 and 33 of the spring 3|.

The central portion 34 of the spring 3| is 55 apertured at 38-33 to accommodate rivets 39 or other like fastening means by means of which the spring 3| is secured to the upper surface of the armature 9. A comparatively large aperture 49 is provided in the central portion 34 of the spring 3| in register with a like comparatively large aperture in the armature 9 to permit passage therethrough of the screw I2 which serves to hold the bridge II and the brass plate ID together. The central portion 34 of the spring 3| is also apertured at 4| to permit passage therei through and into the armature 9 of a bell striker The spring 3| maybe made supporting rod 42. of brass or bronze or other spring material and may be cut or stamped out of a sheet of this material. The projections 31 may be embossings formed on the lower surface of the spring 3|.

As shown in the drawing, the free ends 32-33 of the spring 3| extend parallel to the upper surface of the armature 9 and between the up per surface of the armature 9 and the projecting ends of the poles 5 and 6. When the armature 9 is attracted by one of the poles of the electromagnet and is rocked on its pivotal support, for instance as shown in Fig. 2, a free end of the spring 3| is brought into engagement with the attracting pole and is flexed toward the upper surface of the armature 9, the free end of the spring being progressively flexed from the point of location of the adjacent projections 31 to the outer end of the free end of the spring, the projections 31 serving as a fulcrum for the free end of the spring. The spring pressure built up in the free end of the spring 3| by this flexing movement serves to urge the armature away from the pole of the electromagnet and will return the armature to normal position when the attractive force in the pole is diminished or discontinued. If the projections 31 were not provided, the free ends of the spring would bedefined by the points of securement to the armature and the respective ends of the spring. The free ends of the spring in this case would be less effective in returning the armature to normal position since they would be more flexible. With the projections 31 provided, and located at the positions indicated, the portions of. the spring which serve to return the armature to normal position are comparatively short and stiff and the spring pressure developed in the free end portions when the armature is attracted is greater than would be the case if the projections were not present. The spring structure described and shown therefore is more effective as an'armature return spring than a spring of similar form but not having the projections to serve as fulcrums for the free ends. To merely shorten the spring would not be good practice since the spring serves also as a non-stick element and to be properly efiective as such must be of. sufficient length and width to provide a non-magnetic surface between the poles of the electromagnet and the adjacent face portions of. the armature. The spring 3| being made of nonmagnetic material and extending between the attracted end of the armature and the pole of the electromagnet prevents adherence of the armature to the pole of. the electromagnet due to residual or lingering magnetism in the parts. The spring 3|, therefore, serves as a combined non-stick and return spring element for the armature 9. The particular structure of the spring 3| also serves as an aid in obtaining correct spacing of the armature 9 relative to the poles 5 and 6 of the electromagnet when the ringer is being assembled.

In assembling the ringer a gauge strip of predetermined thickness may be placed between the upper surface of the spring 3| and the poles of the electromagnet and directly above the projections 31. By turning the machine screw I! the armature assembly may. then ,be moved toward the projecting ends of the poles 5 and 6 of the electromagnet to the extentpermitted by the gauge strip. The projections 31 in this instance serve to prevent flattening of the free ends '32 and 33 of. the spring 3| against the upper surface of the armature 9. After the adjustment of. the armaturejhas' been made in the manner "above described the gauge strip may be withdrawn leaving the armature in adjusted position.

Although brass oibronze has been indicated as being suitable material for the spring 3|, it is obvious that other non-magnetic material may be employed insteadwithout departing from the spirit of the invention. While the invention has been shown anddescribedas being applied to a telephone ringer, it is realized that it maybe found applicable tor other electromagnetic devices. The scope of the invention, therefore, is considered as being only limited to the extent indicated inithe following claims; 1 3 a What is claimed is:

i. In .an: electromagnetically operated device, an electromagnet pole, anarmature spaced from said electromagnet pole, a spring 'of sheet material secured to: said armature and extending parallel to said armature and between said electromagnet pole and said armature afree end p portion on said spring spaced from saidarmature and from said electromagnet pole and a projection on said free end portion of sald spring, said projection bearing against said armature and serving as a fulcrum for the free end portion I of said spring when the armature is attracted and the free end portion of said spring is brought into engagement" with said electromagnet pole.

2. In an electromagnetically operated device. electromagnet poles, an armature spaced from said electromagnet poles, a flat spring secured at its central portion to said armature and extending parallel to said armature and between said electromagnet poles and said armature, free ends of" said spring offset from the central por-- tion of the spring and spaced from said armature and from said electromagnet poles'and embossings on the free ends of said spring adjacent the points of offset said embossings extending into engagement with said-armature andserving as fulcrums for the free ends of said spring 'when said armature is operated by means 'ofs'aid electromagnet poles. i i

3. In an electromagnetically operated device, a centrally pivoted armature, a leaf spring of non-magnetic material attached to a central portion of said armature, free ends of said spring ofiset from the plane of the central portion oi said spring and extending in spaced relation with and parallel to said armature and spaced-projections on the free ends of said spring adjacent the points of offset and engaging said armature, said projections serving as combined spacers-and fulcrums for the free ends of said spring by preventing flattening of said'free end portions against said pivoted armature, a spring of non-magneticmaterial attached at its central portion to an upper face of the central portion of said armature, free end portions offset from the central portion of said spring and extending parallel to and spaced from said armature, and a plurality of aligned spaced embossings adjacent each point of ofiset in said spring and within each free end of said spring, said embossings extending downward from the free ends of said spring and into engagement with the upper surface of said armature, said embossings serving as fulcrums for the free ends of said spring when said armature is rocked on its pivotal point and the free ends of said spring are brought into engagement with the pole of an electromagnet.

HAROLD A. BREDEHOFI. 

